1. Field of the Invention
This invention relates to a support material for use in a lithographic printing plate, to a method for the preparation of the support material, and to a lithographic printing plate comprising such support material exhibiting improved press sensitivity and extended shelf-life.
2. Description of the Prior Art
One important characteristic of any presensitized lithographic printing plate is the ability to remain stable and yield reproducible photographic speed performance between the time the plate is manufactured and subsequently used. Yet another important property is the ability of the plate to shed ink from non-image areas during start-up and throughout the useful life of the plate.
U.S. Pat. No. 4,492,616 describes a process for treating aluminum oxide layers by treating the metal surface with an aqueous alkali metal silicate solution and an aqueous solution containing alkaline earth metal ions.
U.S. Pat. No. 3,860,426 describes a lithographic printing plate having a hydrophilic cellulosic subbing layer containing a water-soluble salt of a metal to reduce scumming of the plate in areas in which the printing layer is removed. While these plates have gained widespread commercial acceptance, they have not been found to yield reproducible speed performance between the time the plate is manufactured and used under all storage and handling conditions encountered. Moreover, the printing industry has demanded more stringent requirements regarding press sensitivity in their efforts to minimize variability and waste.
Thus, there is a need for lithographic printing plates exhibiting improved press sensitivity and extended shelf-life.